EP-A 0 141 178 discloses an arrangement for measuring the level of concentration of a substance, with which it is possible to determine levels of concentration of H.sub.2 O.sub.2. The arrangement has a measuring electrode comprising noble metal which is separated from an electrolyte by a lipophilic membrane. In that case the membrane contains lipophilic ions, in particular anions, and/or carrier-bonded ions and is proton-impermeable. In a particular embodiment, contained in the electrolyte space or chamber which is separated from the electrode by the lipophilic membrane is an enzyme which converts a diffusible substance inter alia into H.sub.2 O.sub.2, the concentration of which is measured by the arrangement and thus makes it possible to determine the concentration of the substance.
That arrangement for measuring the concentration of a substance suffers from the disadvantage that the measured parameter varies relatively substantially during the measurement procedure, that is to say it is subject to a certain amount of drift.